Integrated circuits or xe2x80x9cchipsxe2x80x9d have innumerable applications and constitute components which are more or less commonplace depending on the envisaged applications.
A chip is, in itself, a complex assembly formed of several parts, in particular a basic substrate on which the microscopic active and passive components are organised in large numbers and which provide the chip with its functional characteristics.
It is understood, however, that the substrate is not unimportant and that its physical and chemical characteristics are determinant, at least for certain applications.
In the following text, the expression xe2x80x9coriginal substratexe2x80x9d is used to denote the substrate, its composition and its structure, such as it exists before the first manufacturing steps relating more specifically to the microscopic active and passive components of the chip.
The present invention relates, as will be seen below in detail, equally well to the original substrate, to the chip and to the devices with which such a chip can be associated, because of the characteristics which they procure for these devices.
Chips are already known whose microscopic active and passive elements are produced by semiconductor manufacturing processes considered as standard, using high temperatures, of the order of 1,100xc2x0 C., which demand, obviously, that the structure should be compatible with these severe thermal stresses, which is the case of monocrystalline semiconductor substrates, of the silicon type having a thickness of at least 400 xcexcm (micrometres).
This structure is by far the most widespread because it allows chips to cover virtually all electronic applications: microprocessors, memories, etc.
On the other hand, these chips cannot be used in applications which assume that they can be traversed by light because of the fact that the original substrate is not transparent (at least not in the visible spectrum).
Similarly, as the original substrate is, by nature, a semiconductor, it is not insulating and is inappropriate for applications necessitating high frequencies (high frequencies or ultrahigh frequencies) which require a perfect insulation of the functional elements associated with the substrate.
Chips are also known which are manufactured at these high temperatures, but using specific processes which are non-standard and therefore costly, from original substrates comprising a very thin layer (of few fractions of a xcexcm) of monocrystalline silicon semiconductor associated by crystalline growth (epitaxy) on a transparent monocrystalline insulating substrate of the sapphire or corundum type.
Unfortunately, faults are introduced in the epitaxially grown thin layer which results in a detectable reduction in the performance expected from the functional elements.
The original substrate is very expensive and its cost, added to that of the non-standard use, results in prices for the chips produced in this way which are prohibitive for the envisaged applications. In fact, these chips have prominent qualities with regard to their resistance to radiation and their applications are, in practice, restricted to the nuclear field and to the space field which accept high prices because the essential purpose is to achieve the sought goal and not to restrict the cost price, which is obviously not the case in commercial areas in competitive markets.
Certain non-standard manufacturing processes require temperatures lower than those mentioned above, namely less than 600xc2x0 C., which makes it possible to adopt other structures, particularly a very thin layer (a few fractions of a xcexcm) of amorphous or polycrystalline silicon semiconductor deposited chemically in the vapour phase on a transparent insulating silica or glass substrate.
The active elements formed in an amorphous or polycrystalline material are very slow and totally inappropriate for circuits operating in high frequency logic or ultrahigh frequency analogue applications. Optoelectronic devices of known type such as active matrix liquid crystal screens cannot be manufactured in this way in the form of a chip integrating all the screen addressing functions.
There are also semiconductor chips comprising a semiconductor substrate upon which the functional elements are fixed with the interposition of an insulating layer but this layer is too thin to procure a genuine insulation at high frequency and at ultrahigh frequency, because it is only a few xcexcm thick, or even only a few fractions of a xcexcm, which cannot be compared with what an insulating substrate of several hundred xcexcm would be.
There are also semiconductors whose structure comprises on the one hand a thin layer (a few fractions of a xcexcm) of a monocrystalline semiconductor of the silicon type and comprising the very numerous functional elements, and on the other hand a thin insulating layer, this assembly being originally integrated on the surface of a monocrystalline silicon support in order to create a standard non-insulating non-transparent type substrate, known by the abbreviation SOI (Semiconductor On Insulator).
Then, by a complete post-process, this assembly is detached from its original substrate and is then transferred and fixed to another thick (400 xcexcm and more) final insulating and transparent support, by means of an organic adhesive;
After obtaining the actual functional elements according to a standard process, it is necessary to use this post-process according to the following phases:
a) stick the front of the two thin layers on one face of a flat handling dummy, using a temporary glue,
b) mechanically thin down the original opaque support, by removing material in order to eliminate it from the side remote from the dummy,
c) after mechanical thinning, eliminate what remains of this original opaque support by physical-chemical means, until the thin insulating layer is revealed,
d) glue this thin insulating layer on a final insulating and transparent support, generally made of glass or silica, using an organic, insulating and transparent organic adhesive (which could not withstand the high temperature necessary for the manufacture of the functional elements),
e) remove the dummy by unsticking it from the two thin layers.
According to a variant of the post-processing, a dummy is not used but a final insulating and transparent support is used directly, the initial opaque one is thinned and it is removed so that, finally, the assembly of the two thin layers is fixed to the second insulating and transparent support by its face which is generally the external face. This post-processing is very complex and difficult to automate, which results in high cost prices.
The present invention proposes a new solution making it possible to produce chips on an original substrate of the low-cost SOI type, having an insulating and transparent support and whose structure allows the use of standard manufacturing processes.
To this end, the invention relates to an integrated circuit device or xe2x80x9cchipxe2x80x9d, of the type comprising an original support and microscopic active and passive functional elements present in a thin layer of monocrystalline semiconductor material, characterised in that the original support is refractory and transparent and is covered on one of its faces with a thin layer of transparent and insulating inorganic refractory material, this thin layer itself being covered with a thin layer of inorganic monocrystalline semiconductor material, in particular of the silicon or silicon-germanium type, which contains the active functional elements and which supports the transparent passive functional elements, other opaque functional elements being punctually arranged to allow transparent cells to remain, through which light of the visible spectrum can freely pass through the entire chip.
According to other characteristics of the invention:
the original support is made of refractory glass;
the glass has a coefficient of expansion adapted to that of the thin layer of semiconductor material;
the original support is covered on all of its faces with a refractory and transparent layer having a barrier effect with respect to certain chemical elements present in the support, in order to confine them therein;
the original support carries an opaque layer on its face which is remote from the one carrying the semiconductor layer;
the semiconductor layer is formed of monocrystalline silicon or silicon-germanium whose thickness is sufficiently thin that the said layer is transparent;
microelectronic elements such as transistors are disposed on the periphery of the transparent zones;
liquid crystals are integrated with a thin material, in order to constitute a unit structure interposed between the chip itself and a transparent counter-electrode formed by a thin layer applied against a transparent window, this assembly constituting a transmissive screen-chip;
the device is associated with lighting means situated on the side remote from that through which it must be observed, either directly or by projection;
the device is integrated with an apparatus such as a portable radio-telephone;
the device constitutes a detachable plug-in assembly provided with devices for connection to an apparatus such as a radio-telephone;
the device is associated with a spectacle frame, at the rate of one for each eye in a symmetrical and axial but not central arrangement;
the device is associated with a mini-projector with a screen having a decimetric surface area.